1. Field of the Invention
This invention relates to an interface system for watching the status of a stencil printer when printing data generated by a computer is output to the stencil printer.
2. Description of the Related Art
A stencil printer is sometimes connected to a computer by way of an interface system to print on request from the computer. As a printer driver installed in the computer, there has been known one which has function of watching the status of the stencil printer. When printing data are transmitted to the interface system by way of the printer driver from the computer, the interface system analyzes the printing data and converts the data to raster data. The interface system outputs the raster data as page data and the stencil printer prints on the basis of the page data. The interface system is provided with a status control means which sets instruction on the action of the stencil printer on request from the computer. The interface system takes information on whether the stencil printer is in a stopped state, in action, or in an error state as status information through the status control means and stores the information in an updated status memory means. The interface system sends the updated status of the stencil printer on request from the computer. The printer driver of the computer outputs request to switch the direction of data transfer to the interface system when the status information becomes necessary during transfer of the printing data, and the interface system sends the updated status information in a predetermined data length to the computer upon receipt of the request.
During receiving the status information, the printer driver transfers and receives the status information in a fixed format wherein it outputs request to switch the direction of data transfer to the printing data transfer direction after it receives the predetermined data length. Further there has been known a variable format wherein the printer driver watches the time interval between adjacent series of data (time-out period) at a breakpoint of status information from the interface system, recalculates the time- out period each time it receives a series of data, and outputs request to switch the direction of data transfer to the printing data transfer direction after the time-out period lapses.
As the standard of data transmission between the computer and the printer, there have been known a compatibility mode, a nibble mode, a byte mode, an ECP mode and an EPP mode. When the computer and the printer are connected in parallel, the compatibility mode is generally used in the case of one-way communication which is a conventional system. In order to realize two-way communication, the nibble mode is employed as a basic system. That is, when normal printing data are send to the printer from the computer, the printing data is transferred in the compatibility mode and when the computer requires status information on the printer, the status information is transferred from the printer to the computer in the nibble mode. Accordingly, during printing, the printing data and the status information are alternately transferred at predetermined intervals.
In the case of the fixed format, communication of a predetermined amount of data is constantly required even if change in status of the stencil printer is small, which results in low utilization of data. In the case of the variable format, the last time-out period is vain, which also results in low utilization of data when switching between transfer of the status information and that of the printing data is frequent.